Application of copper salts and copper microparticles in polymers and resins for the control of the growth proliferation.
The appearance of multidrug-resistant microorganisms has triggered the search for novel compounds which are capable of combating bacterial proliferation without acquiring resistance as is the case with the agents currently being used (Betancourt et al. 2016).
The development of nanotechnology has permitted the creation of materials which can have dimensions within the order of micrometers and nanometers, materials which show very promising characteristics as antimicrobial agents (Chatterjee et al. 2014). The nano- and microparticles, have the ability to act independently or as transporters of other molecules, and by virtue of their characteristics of surface area, volume, and structure, can trigger biological responses (Chatterjee et al. 2014).
Copper is among the chemical elements used to form nano and microparticles. Copper compounds and complexes have been used in formulations and products for the disinfection of liquids, solids, and human tissues (Delgado et al. 2011).
Different documents from the prior art have described the incorporation of copper compounds and copper nano-/microparticles into solids with the objective of producing a product with antibacterial and/or biocidal properties.
In the case of textile-type materials and fibers, the document U.S. Pat. No. 8,183,167 (B1) discloses fabric substrates which are covalently bonded with copper and/or silver nanoparticles which show antimicrobial activity.
The document U.S. Pat. No. 5,458,906 A presents a method for treating biodegradable substrates with antibacterial compounds, among them, copper. U.S. Pat. No. 7,754,625B2 describes an antimicrobial textile that comprises one or more natural or synthetic fibers or filaments that are combined with an antimicrobial agent, where said antimicrobial agent comprises a predominant quantity of a water-soluble zinc salt in combination with at least one source of antimicrobial silver ions and at least one source of copper ions.
The document U.S. Pat. No. 7,169,402B2 presents an antimicrobial and antiviral polymeric material that has microscopic particles of ionic copper encapsulated in it, which are included in the surface of the product to be formed.
In the document CL201300332 (WO 2014117286 A1) an impregnable matrix of vegetable, animal, or synthetic origin or mixtures thereof in different proportions which contains an antimicrobial compound corresponding to Cu4SO4 (OH)6 is disclosed.
The document CL201500921 discloses a cellulose-based material that incorporates an antibacterial agent corresponding to a copper compound, mixed copper microparticles or nanoparticles. A method for manufacturing a cellulose-based material which includes steps for the addition of copper microparticles or nanoparticles is included.
The document CL 201503652, in turn, presents a translucent adhesive film which shows surface-protecting antibacterial activity, adhesive film which comprises nanoparticles of copper, chitosan, gelatin, and glutaraldehyde.
Various materials have been developed specifically for the food industry for packaging foods. The documents WO 2014001541 A1, WO 2012127326 A1, and WO 2000053413 A1 describes the production of polymeric materials that contain copper particles for the purpose of use in food packaging with antibacterial and/or biocidal properties. The materials envisaged in these documents include copper compounds or copper particles, with copper oxide primary among them.
Although there are several previous antecedents with reference to the addition of copper compounds and copper microparticles supported on different types of carrier or mixtures of them in matrices and polymeric materials to grant antibacterial properties, the proposals vary with respect to the oxidation state of copper. The oxidation state of the copper will influence the solubility of the kind of copper, and, consequently, in the release behavior thereof from the polymeric material; what is more, the different carriers used tend to make the essential particles bulky.
With regards to antibacterial and/or biocidal materials for packaging or containers, it is necessary to produce quick and instantaneous release in the container to inhibit the surface growth of microorganisms on the foods which cause them to deteriorate and are present at the time of packaging (RAM bacteria). Medium-term release is also necessary to inhibit outbreaks caused by the particular handling of each operation, temperature changes, and storage, among other things. In practice, it is therefore necessary that a material include copper microparticles having a solubility (Kps) that enables it's immediate, ongoing, and residual release over time, maintaining concentrations of copper that allow it to have an antibacterial and/or biocidal effect, but which also are copper concentrations which allow avoidance of the toxicity associated with this compound or excess migration to the food products in contact. In other words, a material with improved antibacterial and/or biocidal effect at lower concentrations of copper is required.
The specific composition of the microparticle of the present invention enables translucent materials to be produced, an important characteristic in the case of food packaging materials, because the particle does not have any carrier to support it and render it bulky gives translucency to the material.
In the case of the present invention, the production of a microparticle of copper which comprises 5 types of copper compounds, each having different solubilities (Kps) is proposed. On the one hand, the presence of copper sulfate compounds (Kps=4×10−36), which dissociate instantaneously on contact with moisture—a quick-release copper compound—will make it possible to produce a direct and immediate antibacterial and/or biocidal effect in the material containing it. On the other hand, the presence of copper hydroxide compounds (Kps=2.2×10−14)—a compound with less solubility—will impart to it a bactericidal and/or biocidal effect that is sustained over time. This microparticle offers the advantage that it has the ability to provide 5 different copper compounds, with their own, non-transferable qualities and advantages, which are provided in the same place or physical space upon being introduced into the final polymer or wherever they are placed, providing all of the qualities and advantages of each one of the individual compounds at the same time in the same place and physical space, which is an indispensable condition when low dosages are required, to avoid a loss of translucency and releases of copper that could pass to the products in contact, without diminishing its antibacterial and/or biocidal efficacy, being efficient over time, all in the same place, in a homogeneous form and in contact with foods or other types of products or surfaces where high levels of free circulating copper ions are not required. Thus, the antibacterial and/or biocidal effect of each of the 5 copper compounds can be provided homogenously and at low dosages due to the specific composition of the microparticle according to the present invention.